After not being troubled much for years, I started getting them practically weekly on my commuting bike . Eventually, despite diligent checking after each ouncture, I realised there was a nick in the inside of the tyre leading to a lumpy bit. It was wasn't a thorn shard of glass but tyre damage, which though small (2mm maybe) was causing a lump, which in turn, appeared to be causing punctures. Bought a new tyre and problem solved. The original tyre's partner is still on the bike so there was nowt wrong with the brand of tyre and it had plenty of wear left in it otherwise. My bet is you've a similar subtle problem with your tyre.
Of course, you do need to make sure tyres are properly inflated (snake bite punctures are indicative of under inflation) and that there isn't a patch of thorns / hedge clippings / glass
shards you're repeatedly crossing on a regular route